Significant Accounting Policies (Schedule Of Rental Property Improvements) (Details) - USD ($) $ in Thousands |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2018 |
Dec. 31, 2017 |
|
| Property, Plant and Equipment [Line Items] | ||
| Land held for development (including pre-development costs, if any) | $ 508,342 | $ 483,432 |
| Development and construction in progress, including land | 405,853 | 535,971 |
| Total | 914,195 | 1,019,403 |
| Buildings and improvement | 220,700 | 188,100 |
| Development [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Land | $ 49,600 | $ 77,000 |